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The intestinal tract in strict carnivores is much shorter than in other animals. And unlike dogs, cats eat the intestinal tract of their prey last, or not at all, thus avoiding the plant fiber of the intestinal contents. These facts have led scientists and veterinarians to assume that cats need little fiber in their diet. The assumption being that a diet devoid of plant fiber is a non-fiber diet. But plants are not the only source of fiber.

Animal Fiber

The undigested fur, bone, cartilage, tendon and ligaments of prey also constitute intestinal fiber. The undigested hair from the fastidious grooming of cats also provides intestinal dietary fiber. Animal fiber may be extremely important in the nutrition of strict carnivores. A recent study in cheetahs has highlighted these insights.

The Study

Scientists alternately fed 14 captive cheetahs diets consisting of raw, supplemented butchered beef without bones and whole raw rabbits with fur. Each diet was exclusive for an entire month. The scientist monitored various fecal fatty acids and chemicals. What they found was that when cheetahs were fed whole rabbits the fatty acid profile in the feces was more favorable and resulted in a significantly decreased production of toxic metabolic chemicals. The scientist made no mention of fecal volume or consistency differences between the two diets. This study pioneers the concept of animal fiber and the digestive health of captive and domesticated cats. It also raises the question of whether substituting plant fiber in our cats’ diets adequately substitutes for animal fiber for intestinal health.

Plant Fiber in Commercial Cat Food

Oddly, cats share nearly the same spot on the mammal food chain as rabbits. Lacking the stamina to outrun their predators, wild cats have relatively short life spans and high infant mortality. That is why they are induced ovulators (if they have sex they get pregnant) like rabbits and easily become pregnant even while nursing.

As prey, cats have developed biological and behavioral traits to minimize the attention of predators. The feces or “scat” of wild cats is very small and not highly odiferous (smelly). Like their urine, they bury it to further hide any scent. Contrast that with the stool of cats on commercial dry food. Stool in cats fed those diets have huge stool “logs” that can be smelled two rooms away. Granted, this is not important for inside cats but such stool in outdoor or indoor/outdoor cats could draw the attention of dogs and coyotes. Without study, we have no way of knowing whether the substitution of plant fiber for animal fiber has the same beneficial effect in the colon that the cheetah study found. Are we creating larger amounts of stool without knowing its benefit or lack of benefit?

The grooming behavior of cats results in the ingestion of large amount of fur or animal fiber. Current owner preoccupation with preventing or blaming all digestive upsets and coughing on "hairballs" may actually be contrary to the digestive health needs of the cat.

In 29 years of veterinary practice, some feline exclusive, I have yet to remove a hairball from the intestine or esophagus of a cat. Sure it happens, but not to the extent to warrant the present level of concern. Why? Cats fed dry diets generally vomit much more than cats fed canned or meat diets. In addition to food, vomiting also brings up stomach fur. These cat parents assume the hairball is causing the vomiting. Hence all of the vomited Vaseline treated cat kibble to ward off hairballs. In light of the cheetah study the observation should be turned around. The dry food is causing the vomiting and preventing the hair to reach the intestines as intended. Owners who decrease or eliminate dry food from their cat’s diet almost always experience less vomiting and fewer hairballs in their pets, despite the same degree of grooming and hair consumption. Going back to the study, maybe plant fiber is not a good substitute for animal fiber and has unintended consequences in strict carnivores.

More Study

Obviously much more study is needed in this area. It would certainly help us understand the nutritional needs of these interesting carnivores that share our lives. I hope you found this study as interesting and stimulating as I did.

I was under the impression that vomiting was a way of cleaning out their system. Surely cats in the wild sometimes vomit.

It's fascinating that the cat family eats the intestines of their prey last or not at all.

It seems like some years ago one of the pet food companies advertised that their food would be better digested. The result would be more compact stool, less in the litter box. Considering how much plant additive that company uses, it would be interesting to compare that company's studies with this one.

Maybe it's not the fiber in the diet, although I do believe that cats should have some fiber, but the moisture content of canned food. I DO chop up wheat grass and add it to my cat's wet food and they love to graze on the grass too. My cats get a lot of canned food and they very rarely, if ever, have hairball problems. I decided when I got the 2 little girls that I would try to feed them a diet based more on canned food and a lot less dry food. It's an experiment to see if all of the kidney failure my previous cats died from was due to the carbohydrate content of the dry food and the fact that they were slightly dehydrated all of the time. My oldest cat (15+) gets mostly wet food and he's doing great with good bloodwork.

For your benefit, Dr Tudor, there HAVE been studies done on this subject. An example is the very famous one that studied ingredients being put into both wet and dry foods, which I am glad to see as trying to say that a food is better because it is "dry" or because it is "wet" just doesn't cut it in my world where nutrition based upon ingredients in individual foods are studied: http://jn.nutrition.org/content/128/12/2717S.full.pdf+html (see Table 6 for comparisons). Here we limit the amount of canned food we use because it all seems to contain guar gum, and guar gum runs food through a cat to the point of causing malnutrition. The dry food we use for grazing, as our cats are naturally built to do, has beet pulp, and possibly the amount of it in the food is enough to keep motility in the gut healthy and prevent hairballs as we never see them here, using a high protein, low fat, (no obesity or weight related illness), low carb food. I agree with you that foods creating higher fatty acid content in feces are going to produce less "smell", but I am not willing to risk the consequences in our altered cats.

Dr. Zoran has been pointing out in her presentations, since 2006 when studies on gonadectomies have been published, that cats are "dropped into menopause" and I can't see how it is appropriate to compare eating behaviors of our sedentary house cats with wild cheetahs. Not only do we have to compensate for the fact that our cats are altered, but also, small felids, unlike cheetahs, are designed to eat 12 to 20 meals per day, based on a number of references provided by the National Research Council in their latest book.

As you are a specialist in obesity/weight issues, I am am surprised you haven't encountered the fact that the Royal Canin Diabetic food, recommended on occasion by both Deb Zoran and Jacquie Rand for obesity/diabetes related issues, DOES avoid hairballs because of the appropriate fermentable fiber content.

While I can't find it at the moment, there is also research out there showing, in the data collected, that motility of foods through the gut is better with fiber used in good dry foods.

For anyone wanting a good understanding of a small felid's intestinal tract and health issues accompanying the use of commercial foods, I like to use the following site as a reference: http://www.felineconstipation.org While my training was in glycemic control of humans, this person's was, and continues to be, in gut bacteria -- fascinating subject.

Thought it would be appropriate to provide at least one reference regarding my personal bias where canned foods are concerned.....
http://jas.fass.org/content/73/8/2329.full.pdf Sunvold et al, 1995. Dietary fiber for cats: in vitro fermentation of selected fiber sources by cat fecal inoculum and in vivo utilization of diets containing selected fiber sources and their blends.
page 2334 quote from last paragraph: "For example, substrates such as locust bean gum, guar gum, and citrus pectin were highly fermentable"
page 2338, second paragraph quote: "Dietary nutrient utilization is not impared when fiber is added to cat diets, except when rapidly fermentable and highly viscous sources of fiber are added. Providing a source of moderately fermentable fiber in cat diets promotes the formation of fermentation end prducts that may be important in maintaining the health of the lower gastrointestinal tract of cats."

There are lots of other such papers, but I am trying to find the paper that showed dry foods actually utilize nutrients better. I assume it is because the appropriate fermentable fiber is being used. I will post it if I find it.

@CathyA, I am not sure what you are referring to? Could you please clarify? Is it the fiber in soy that concerns you?

The grazing food we use, that is in the product recommended by experts in feline nutrition, has soy as a source of both secondary fiber, (beet pulp beint the main), and it provides genistein, which reduces blood sugar readings in diabetics I would rather see soy, a legume, as a filler, providing some added fiber, than high fat foods offered for our pets.

I also can't understand why you are suggesting that soy fiber would be irritating? I am always trying to figure out why the low calorie food we feed for grazing -- with soy in it -- seems to prevent any furballs. In April we took in another foster cat that was barfing furballs on almost a daily basis, and in two months she has stopped completely, so I really don't understand your comment and would love some clarification, preferably with some scientific references as to why you think soy is an issue?

The problem with relying on dietary sources of fiber is that most people don’t eat a diet high in fiber. For people like me whose diets are less-than-rich in fiber, I recommend the Lady Soma Fiber Cleanse. Its a fiber supplement (not a cleanse) because its all-natural and has natural (herbal) sources such as ground flaxseed and psyllium husks, and provides at decent amount of fiber per serving. This product saved me. You should give it a try - I dont get the fiber that I should when I dont use it.

The best fermentable fibres for dogs and cats are rice bran and beet pulp: http://jn.nutrition.org/content/128/12/2717S.full.pdf+html (Table 6). Our companion animals are quite different in dietary requirements to humans, and even with humans flax can be too rough on the villi, causing damage because whole flax doesn't break down in the body. It was either the Iams symposium papers or the NRC book on page 38 that stated the following: "Fiber digestibility was greatest for cats consuming a diet containing beet pulp (a moderately fermentable fiber), a diet containing the highly fermentable blend of fibers and a diet containing a combination blend of fibers designed to provide moderate fermentation (beet pulp, rice bran, citrus pectin, and carob bean gum)"

Personally, I do just fine with the foods I eat and have no need for artificial aids, thankyou.